Topband: DX-100 adventure

[Bill Cromwell]

On 12/06/2013 10:22 AM, ZR wrote:
>
> The last DX-100 I rebuilt for a customer (I use various Johnsons and 
> other makes) had the fairly common 5R4 sockets arcing from whatever 
> contanimation they are afflicted with. NOS replacements still wrapped 
> up in boxes worked fine; Ive heard of Chinese sockets having a lead 
> content, never tried them. Dont even think of going SS.
> Change the LV to choke input, there is too much voltage on the tubes 
> for reliability, especially the 6146/1625 screens. Increase the filter 
> cap to 47uF and also the HV output cap to reduce ripple. Replace all 
> electrolytics, dont waste time even thinking about it.
>
> I have a long list that I can get to you and not take up space 
> here...if this even gets thru censorship.
> The fixed padders in the VFO go up in value and tracking cant be 
> achieved. New silver micas matced to 1-2% of the schematic worked 
> fine. I also used a 6AH6 VFO and zenered the plate and screens at 
> 100V. With all good tubes drive was more than sufficient even on 10M 
> and drift was reduced. Keep the 6146 drive down to about 3-4 ma total, 
> more does nothing but cook them and AM is still well modulated with 
> some basic audio circuit changes.
>
> Carl
> KM1H
>

Hi Carl,

Thanks for your comments. Those caps are definitely on my agenda. I have 
used the solid state swap for the rectifiers in other power supplies 
with no detrimental effects but that always included making sure the 
higher voltages wouldn't meet any under-rated parts. I did find the 5R4s 
bad - one with a dead short. I just happened to have two more that were 
good in the spares bin. No solid state repacements - this time. The 
DX-100 is old and has been hacked several times in the past. Some of the 
past workers (and maybe me too) left some "elephant tracks" under the 
chassis. I'm cleaning up some sloppy connections as I go along, too. 
Fortunately I have a hard copy of the manual with prints and all. When I 
get it so it's safe to run I'll make the voltage checks to help find 
resistors out of spec, etc.

I have several replies in private email and all of the comments say 
similar things. So far nobody has mentioned that original power cord 
with the fuses in the plug. I will make that go away, too.

73,

Bill  KU8H